Apparatus such as aircraft engines, turbines, and pumps typically include at least one shaft that normally rotates at a relatively high speed. An apparatus such as an aircraft jet engine may include multiple shafts that normally operate at high speeds while passing through several zones of varying pressures. A jet engine creates thrust by compressing atmospheric air, mixing fuel with the compressed air and igniting it, and passing the ignited and expanded air/fuel mixture through a turbine. Zones having various pressures exist throughout the length of the engine. These zones must typically be sealed from one another in order to allow the engine to operate, and in particular to increase the efficiency of the aircraft engine. In addition to the high rotational speeds of an aircraft engine shaft, axial and radial shaft movement increases the difficulties associated with maintaining effective seals throughout the lifetime of the engine. An effective seal must be able to continuously accommodate both axial and radial shaft movement while maintaining the seal. When rigid seals are installed, shaft movement can create excessive wear leading to an ineffective seal.
One type of seal that has been increasingly used in recent years in order to accommodate the shaft movement mentioned above is a brush seal. Numerous configurations of brush seals for use with shafts are known in the art. Brush seals typically include a ring-shaped body member or holder having bristles extending therefrom. The bristles may extend radially inwardly or radially outwardly from the holder. In a typical configuration, the bristles contact the rotating member while the holder is fixed to a stationary support member. The bristles are flexible enough to allow the shaft to rotate against it, and to move both axially and radially, while effectively maintaining a seal. The bristles may be constructed from a variety of materials. One common construction is the use of metal or ceramic bristles that are held by the holder at one end and are free and in contact with the moving shaft at the other end. Another construction includes a series of interlocking fingers.
In the past, brush seals have been used unsuccessfully in apparatus such as aircraft engines, turbines, and pumps because of the high shaft speeds required by these devices. The high shaft speeds often cause the bristle portion contacting the shaft to rapidly deteriorate due to shaft eccentricity and the amount of heat that is quickly generated at the shaft/brush interface. When the bristle portions are constructed from a stronger material (e.g. ceramics), the section of the shaft contacting the bristle portion undesirably wears causing the entire shaft to require replacement or rehabilitation. The frictional engagement of the brush with the rotating member also creates the undesirable generation of heat.
Accordingly, it is an object of the invention to provide an improved seal for use between relatively rotatable members which overcomes the disadvantages discussed above. Specifically, the improved seal assembly according to the invention cooperates between a pair of relatively rotatable members for creating a sealing relationship between areas of high and low pressures. The seal assembly includes a face seal structure nonrotatably associated with one of the members and defining thereon an annular sealing face, and an annular brush which includes a plurality of bristles having free ends in sealing contact with the other member to form a first seal between the areas of high and low pressures and to cause rotation of the brush along with the other member. Further, the brush includes thereon an annular sealing face disposed and axially adjacent and opposed face-to-face relationship with the annular sealing face of the face seal structure to form a non-contacting second seal between the areas of high and low pressures.
Another aspect of the invention resides in a seal assembly cooperating between relatively rotatable inner and outer members for sealing between areas of high and low pressures, the seal assembly including a face seal structure nonrotatably associated with one of the inner and outer members and defining thereon first and second annular sealing faces. The assembly further includes an annular brush disposed between the inner and outer members which includes an annular array of bristles having free ends in sealing contact with the other member to form a first seal between the areas of high and low pressures and to cause rotation of the brush along with the other member. The brush includes thereon third and fourth annular sealing faces disposed in axially adjacent and opposed face-to-face relation with the respective first and second annular sealing faces of the face seal structure to form a noncontacting second seal between the areas of high and low pressures.
Yet another aspect of the invention resides in a seal assembly cooperating between a housing member and a shaft rotatable relative thereto for creating a sealing relationship between areas of high and low pressures. The seal assembly includes a face seal structure nonrotatably associated with the housing and defining thereon an annular sealing face, and an annular brush surrounding the shaft for rotation therewith and having a plurality of bristles disposed in an annular array about the shaft. The brush includes an annular holder with bristles mounted thereon such that free ends thereof are in sealing contact with the shaft to form a first seal between the areas of high and low pressures. The holder defines thereon an annular sealing face disposed in axially adjacent and opposed face-to-face relation with the annular sealing face of the face seal structure. In addition, the face seal structure includes a passage therein in communication with a gas source for directing a flow of gas between the opposed sealing faces to form a noncontacting second seal between the areas of high and low pressures.
The advantageous arrangement of the present invention, and the objects and purposes thereof, will be apparent to persons familiar with seals of this general type upon reading the following description and inspecting the accompanying drawings.